TEMPE, Ariz. — America West and US Airways finalized their union Tuesday, combining to form the nation’s fifth-largest domestic carrier.

“Today we start a new chapter in aviation history,” Doug Parker, chief executive of the newly combined company, said in a news release.

Although the airlines can now operate as one carrier, they said passengers should continue to book directly with each airline as they did before the deal closed.

The airlines are still operating separate Web sites and still have two reservation systems. Flight crews, maintenance and safety procedures for each airline will also remain separate for some time.

The goal of the deal was to form a stronger airline that would compete better with lower-cost rivals such as Southwest Airlines Inc. and JetBlue Airways Corp.

Arlington, Va.-based US Airways has a strong presence on the East Coast and in the Caribbean. America West, based in Tempe, operates across the West from hubs in Phoenix and Las Vegas.

Even though America West is considered the financially stronger company, the US Airways name will survive.

Beginning early next year, America West planes will begin sporting their new US Airways paint schemes. The company will operate 411 aircraft at first, but that number will decrease by 51 as the company returns planes to leaseholders.

US Airways received final approval on Sept. 16 to exit bankruptcy protection for the second time in three years, paving the way for it to be purchased by America West.

The deal will be funded by $1.5 billion in new capital from a variety of investors, including the European aircraft maker Airbus.